Unix And Shell Scripting

Unix & Shell Scripting Presenter: Jaibeer Malik August 6, 2004

Agenda
Objectives
UNIX
Shell Scripting
Questions
Feedback

Session Objectives
Understand the basics of Unix Operating Environment
Understand the basics of Shell Scripting

Unix History
History of the Unix Operating System:
- Beginning at AT&T Bell Laboratories
- Kenneth Thompson
- Dennis Ritchie
- Berkeley: The Second School
- BSD UNIX
- Stallman and Torvalds
- GNU and LINUX

Unix Why???
There are only two kind of people
who understand 0 1 and who don’t understand
01010101010101010101010101010101010101010101010101010
The features that made UNIX a hit from the start are:
Multitasking capability
Multi-user capability
Portability
UNIX programs
Library of application software

ARCHITECTURE

ARCHITECHTURE
The UNIX system is functionally organized at three levels:
The kernel, which schedules tasks and manages storage;
The shell, which connects and interprets users' commands, calls programs from memory, and executes them; and
The tools and applications that offer additional functionality to the operating system

Solaris File System Tree

Navigating The File System
pwd: Checking your Current Directory
cd: Changing Directory
mkdir: Making Directories
rmdir: Removing Directories
ls: Listing Files

General-Purpose Utilities
banner: Display a Blown-up Message
cal: The Calendar
date: Display the System Date
who: Login Details
tty: Knowing Your Terminal
man <command>: Displays help on <command>
apropos <keyword>:locates commands by keyword lookup
whatis <command>: Brief command description

Handling Files
cat: Displaying and Creating Files
cp: Copying a File
rm: Deleting Files
mv: Renaming Files
more: Paging Output
lp: Printing a File
file: Know the file types
wc: Line and Word and character counting
split: Splitting a File into Multiple Files
cmp: Comparing two files

File Attributes
ls –l: listing File Attributes
ls –d: Listing Directory Attributes
stat: Display File Permissions
chmod: Changing File Permissions
chown: Changing Ownership
chgrp: Changing Group
chsh: Changing Shell
ln: Links
umask: Define Defaults File Permissions for a User

The Environment
env: Displays Environment Properties
.profile: The Script Executed During Login Time
PWD: Know your Current Directory
HISTSIZE: Define History Size
LOGNAME: Login Name
SHELL: Your Default Shell
HOME: Define Home Directory
PATH: Declare Path
MAIL: Declare Mail Directory Path
alias: Define short-hand names for commands

The Process
ps: Process Status
<command> &: To run a process in Background
bg: To run a process in Background
fg: To run a process in Foreground
kill: Premature Termination of a Process
nice: job execution with low Priority
at and batch: Execute Later
cron: Running jobs Periodically

Communication And Electronic Mail
write: Two-way Communication
mesg: Your Willingness to Talk
talk: Splits the screen into two windows for chatting
mail: The mailer
news: To read news messages
elm: A screen-oriented mail handler
pine: Another mail program
finger: Details of Users

Networking
telnet: Remote Login
ftp: File Transfer (protocol)
rlogin: Remote Login Without Password
rcp: Remote File Copying

System Administration
useradd: Adding Users
/etc/passwd: User Information
/etc/shadow: Encrypted Passwords
userdel: Removing Users
fsck: File System Checking
df: Checking disk size
du: Checking file size
groupadd: Adding Group
groupdel: Deleting Group
groupmod: Modifying Group

The Shell
The following table shows the default system prompt and superuser prompt for the C shell, Bourne shell, and Korn shell.

Shell Scripting
A universal convention is that the extension .sh be used for shell scripts (or shell programs or shell procedures ).
The scripts can be executed in two ways:
$ chmod +x <filename.sh>
$ sh <filename.sh>
read: For taking input from the user
Example: $ cat example1.sh
#First Simple Example to print the standard input from the user to the standard output.
echo “Enter Your Name: “
read name
echo “Your name is: $name”

Shell Scripting (Contd..)
When arguments are specified with a shell procedure, they are assigned to certain special “variables” or rather positional parameters.
$1,$2,etc. The positional Parameters
$* Complete set of positional parameters as a single string
$# Number of arguments specified in command line
$0 Name of executed command
$? Exit status of the last command
$! PID of last command

Example: $ cat example2.sh
#Example to print the standard input from the user to the standard output using positional parameters.
echo “Program: $0
The Number of Arguments Specified is $#
The Arguments are $*”
echo “Your Name: $1 Your Extension Number: $2”
Example: $ example2.sh Jai 5630
Program: example2.sh
The Number of Arguments Specified is 2
The Arguments are Jai 5630
Your Name: Jai
Your Extension Number: 5630

Shell Programming (Contd..)
The && operator delimits two commands; the second command is executed only when the first succeeds.
The || operator delimits two commands; the second command is executed only when the first fails.
The exit statement is used to prematurely terminate a program.
The if Conditional
if condition is true
then
execute commands
else
execute commands
fi

Relational Operators
-eq Equal to
-neq Not equal to
-gt greater than
-ge greater than or equal to
-lt less than
-le less than or equal to
test uses certain operators to evaluate the condition on its right, and returns either a true or false
test $x –eq $y or [$x –eq $y]
String tests used by test
-n stg true if string stg is not a null string
-z stg true is string stg is a null string
s1 = s2 true if string s1=s2
s1! = s2 true if string s1 is not equal to s2
stg true if string stg is assigned and not null

File-related tests with test
-e file true if file exists
-f file true if file exists and is a regular file
-r file true if file exists and is a redable
-w file true if file exists and is a writable
-x file true if file exists and is a executable
-d file true if file exists and is a directory
-s file true if file exists and has a size greater than zero

The case conditional
case expression in
pattern1) execute commands;;
……
esac
The while loop
while condition is true
do
execute commands
done

The for loop
for variable in list
do
execute commands
done
Example:
$ for x in 1 2 4 5 #list has 4 strings
do
echo “ The value of x is $x”
done
The value of x is 1
The value of x is 2
The value of x is 4
The value of x is 5

The here document symbol (<<) is used sometimes when we need to place the data inside the script.
The here document symbol (<<) is followed by the data and a delimiter.
shift transfers the contents of a positional parameter to its immediate lower numbered one.
When set –x is used inside a script, it echoes each statement on the terminal, preceded by a + as it is executed.

Example
bash-2.03$ cat example3.sh
IFS="|"
while echo "Enter Department Code: "
do read dcode
set -- `grep $dcode data`
case $# in
3) echo "Department name : $2 Emp-id of head of dept : $3"
shift 3 ;;
*) echo "Invalid Code" ; continue
esac
done
bash-2.03$ cat data
01|accounts|6213
02|admin|5423
03|marketing|6521
04|personnel|2365
05|production|9876
06|sales|1006

Example (Contd…)
bash-2.03$ bash example4.sh
Enter Department Code: 99
Invalid Code
Department name : accounts Emp-id of head of dept : 6213
Department name : sales Emp-id of head of dept : 1006 Enter Department Code:

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Unix And Shell Scripting

by Jaibeer Malik on Sep 22, 2009

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Unix And Shell Scripting — Presentation Transcript